add validation to CLI and try-with block to add-grid.

Make minor spelling and editing fixes to errr
or messages.

DeathSocket/GridPainter.fs

@@ -13,6 +13,5 @@ namespace DeathSocket
                     validateFilePath |> ignore
                     drawGrid spec |> ignore
                 with
-                | :? FileNotFoundException as ex -> printfn"%s" ex.Message
-            }
-            
+                | :? FileNotFoundException as ex -> printfn "File could not be found at %s" ex.Message
+            }

DeathSocketCLI/Commands.fs

@@ -1,17 +1,23 @@
 namespace Commands
 
     module ConsoleCommands =
-        open DeathSocket
-        open System.Drawing
+        open System
+        open DeathSocket.GridPainter
+        open Validation
+        open System.IO
+
+        let showEndOfCommandMessage = "[INFO.] Execution completed."
 
         let test () = "Death Socket is working."
 
-        let ``add-grid`` imgPath numRows numColumns pWidth (colour: string) newPath =
-            let spec =
-                { originalPath = imgPath
-                  savePath = newPath
-                  colour = Brushes.Red
-                  penWidth = pWidth
-                  rows = numRows
-                  columns = numColumns }
-            GridPainter.applyGrid spec |> Async.RunSynchronously
+        let ``add-grid`` imgPath numRows numColumns pWidth colour newPath =
+            try
+                printfn "[INFO.] Adding grid to image..."
+                buildSpec imgPath numRows numColumns pWidth colour newPath
+                |> applyGrid
+                |> Async.RunSynchronously
+                showEndOfCommandMessage
+            with
+            | :? FileNotFoundException as ex -> "[ERROR] No file was found at " + ex.FileName
+            | :? ArgumentException as ex -> "[ERROR] Invalid argument: " + ex.Message
+            | _ as ex -> ex.Message

DeathSocketCLI/DeathSocketCLI.fsproj

@@ -46,6 +46,7 @@
   <Import Project="$(FSharpTargetsPath)" />
   <ItemGroup>
     <Compile Include="AssemblyInfo.fs" />
+    <Compile Include="Validation.fs" />
     <Compile Include="Commands.fs" />
     <Compile Include="Program.fs" />
     <None Include="App.config" />

DeathSocketCLI/Validation.fs

@@ -0,0 +1,41 @@
+module Validation
+
+    open DeathSocket
+    open System.Drawing
+    open System
+
+    let colourList =
+        [ "blue", Brushes.AliceBlue
+          "brown", Brushes.Brown
+          "black", Brushes.Black
+          "gray", Brushes.Gray
+          "green", Brushes.Green
+          "purple", Brushes.Purple
+          "red", Brushes.Red
+          "white", Brushes.White
+          "yellow", Brushes.Yellow ]
+          |> Map.ofList
+
+    let isColourValid (colour: string) =
+      colourList
+      |> Map.containsKey (colour.ToLower())
+
+    let parseColour colour =
+        match (isColourValid colour) with
+        | true ->
+            colourList 
+            |> Map.find (colour.ToLower())
+        | false ->
+            invalidArg "Colour"
+                (String.Concat("The colour specifed is invalid.\n",
+                    "Please use the 'list-colours' command to see what you can use."))
+
+    let buildSpec imgPath numRows numColumns pWidth colour newPath =
+        let spec =
+            { originalPath = imgPath
+              savePath = newPath
+              colour = parseColour colour
+              penWidth = pWidth
+              rows = numRows
+              columns = numColumns }
+        spec